Welcome to Know Your Lore, where each week Elizabeth Wachowski and Alex Ziebart bring you a tasty little morsel of lore to wrap your mind around. Sweet, sweet lore. Mmmm.
The Defias Brotherhood is something that I'm sure both factions have at least a little familiarity with, though the Alliance most definitely has more exposure to them. There aren't many Horde questlines that will give you a brush with this faction of bandits, but even my Horde friends take a trip to Westfall to check out the Deadmines every now and then.
I don't blame them, either. Not only is the Deadmines an awesome instance, the Defias Brotherhood also has quite the interesting background. While there are superhuman entities involved in their story, it isn't laid on as thick as in other Warcraft plotlines. Theirs is more a story of political and social unrest, and the power of manipulation. I would go as far as to say this is part of the single largest plotline in Warcraft currently, spanning half a dozen zones, three expansions, a comic series, and involving at least five different major factions.